1. Field of the Invention
The present invention relates to a high-temperature oxide superconductor exhibiting a superconducting property when cooled with liquid helium or liquid nitrogen, a superconducting wire, a coil using the wire, and a method of producing the wire and coil, more particularly to an oxide superconductor, superconducting wire and coil having a high critical current density even in a high magnetic field.
2. Description of Related Art
Prior art high-temperature oxide superconducting wires are known to have a high critical current density of 1,000 A/m.sup.2 or higher at a liquid nitrogen temperature by flattening the cross-sectional structure through such a pressing technique, such as rolling, as disclosed in Japanese Journal of Applied Physics, 1988, Vol. 27, No. 2, pp. L185 to L187 and Japanese Journal of Applied Physics, 1988, Vol. 27, No. 12, pp. L2345 to L2347.
Furthermore, Japanese Patent KOKAI (Laid-Open) No. 63-252310 discloses a method of producing a homogeneous superconductor composite tape or wire, which comprises plastically forming a composite body comprising a metal sheath and an oxide superconductor, and uniformly heating the oxide superconductor in a furnace, melting part or the whole of the oxide superconductor. In this method, however, the crystal structure of the oxide superconductor is not so changed and the critical current density is not improved in a magnetic field.
The prior art as mentioned above does not take an account of the critical current density in a magnetic field and is accompanied with such a problem that the critical current density is greatly reduced when a small amount of external magnetic field is applied.